In recent years, lithium secondary batteries have been widely used as driving power supplies for small electronic devices such as mobile telephones, notebook-size personal computers and the like. A lithium secondary batteries are mainly constituted of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution containing a lithium salt, in which a carbonate such as ethylene carbonate (EC), propylene carbonate (PC) and the like are used as the nonaqueous electrolytic solution.
As the negative electrode for the lithium secondary battery, known are metal lithium, and metal compounds (simple metal substances, oxides, alloys with lithium, etc.) and carbon materials capable of absorbing and releasing lithium; and in particular, lithium secondary batteries comprising a carbon material such as coke, artificial graphite, natural graphite and the like capable of absorbing and releasing lithium have been widely put into practical use.
For example, it is known that, in a lithium secondary battery using a highly-crystallized carbon material such as natural graphite, artificial graphite or the like as the negative electrode material therein, the solvent in the nonaqueous electrolytic solution decomposes through reduction on the surface of the negative electrode in charging, and even EC widely used as a solvent for nonaqueous electrolytic solution may partly decompose through reduction during repeated charging and discharging, therefore causing deterioration of battery performance such as battery capacity and cycle property.
Further, it is known that a lithium secondary battery using, as the negative electrode material therein, lithium metal or its alloy, or a simple metal substance such as tin, silicon or the like or its oxide, may have a high initial capacity, in which, however, the negative electrode material may be powdered during cycles and, as compared with a negative electrode of a carbon material, it may accelerate the reductive decomposition of the solvent of the electrolytic solution, therefore greatly deteriorating battery performance such as battery capacity and cycle property.
On the other hand, in a lithium secondary battery comprising, for example, LiCoO2, LiMn2O4, LiNiO2 or the like as the positive electrode therein, when the solvent in the nonaqueous electrolytic solution has a high temperature in a charged state, then it partly decomposes through oxidation locally in the interface between the positive electrode material and the nonaqueous electrolytic solution, and the decomposed product interferes with the desired electrochemical reaction in the battery, therefore deteriorating battery performance.
As in the above, the decomposition of an electrolytic solution on a positive electrode and a negative electrode brings about gas generation therearound to swell the battery, or brings about gas retention between a positive electrode and a negative electrode to interfere with lithium ion movement, therefore being a cause of deteriorating battery performance. Despite of the situation, electronic appliances equipped with lithium secondary batteries therein are in a stream of further increase in the power consumption and, with that, the capacity of lithium secondary batteries is being much increased, therefore bringing about problems in that the electrolytic solution is being much more easily decomposable and the battery characteristics such as cycle property are more worsened.
Patent Documents 1 and 2 disclose a nonaqueous electrolytic battery in which the nonaqueous electrolytic solution comprises, as dissolved therein, a methoxybenzene-based compound partly substituted with a fluorine atom or the like, proposing a method of evading thermal runaway by redox reaction in an overcharged state. However, these do not refer at all to cycle property, and are therefore not on a satisfactory level.
Patent Document 3 and Patent Document 4 disclose a nonaqueous electrolytic solution with methyl benzoate or vinyl benzoate dissolved therein, proposing a battery effective for the affinity to a carbon material and for the initial charge-discharge efficiency. However, these do not refer at all to cycle property, and are therefore not on a satisfactory level.
Patent Document 5 discloses a method for producing, as a production material for antimicrobial agents, methyl 3-methoxy-2,4,5-trifluorobenzoate from 3-methoxy-2,4,5-trifluorobenzoic acid, using dimethyl sulfate.
Patent Document 6 discloses a lithium secondary battery comprising a nonaqueous electrolytic solution of, as dissolved therein, methyl benzoate partly substituted with a fluorine atom or the like, indicating that the lithium secondary battery has a higher discharging capacity than a lithium secondary battery comprising a nonaqueous electrolytic solution of, as dissolved therein, methyl benzoate not substituted with a fluorine atom or the like. However, even the battery is not still on a satisfactory level in point of the initial battery capacity and the cycle property thereof.    [Patent Document 1] JP-A 10-308236    [Patent Document 2] JP-A 2000-156243    [Patent Document 3] JP-A 8-293323    [Patent Document 4] JP-A 2000-299127    [Patent Document 5] JP-A 3-127755    [Patent Document 6] JP-A 2000-323169